IEEE C80216n-11/0092
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
Determining alternative path in Path Discovery and Management
Date
Submitted
2011-05-10
Source(s)
Hoang Vinh Dien, Ming-Tuo Zhou, Xin
Zhang, Liru Lu (Alina), Masayuki Oodo,
Hiroshi Harada
E-mail: hvdien@nict.com.sg;
mingtuo@nict.com.sg; zhangxin@nict.com.sg;
liru@nict.com.sg; moodo@nict.go.jp;
harada@nict.go.jp
National Institute of Information and
Communications Technology (NICT)
Re:
Call for contributions for the 802.16n Amendment Working Draft
Abstract
This provides a proposal of establishment and maintenance of alternative path in 802.16n
networks (Original document in Session #72: C80216n-11_0026.doc)
Purpose
To be discussed and adapted by TGn for draft 802.16n AWD
Notice
Copyright
Policy
Patent
Policy
This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It
represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for
discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material
contained herein.
The contributor is familiar with the IEEE-SA Copyright Policy
<http://standards.ieee.org/IPR/copyrightpolicy.html>.
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<http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and
<http://standards.ieee.org/guides/opman/sect6.html#6.3>.
Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and
<http://standards.ieee.org/board/pat>.
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IEEE C80216n-11/0092
A Proposal for determining alternative path in path management of
802.16n-GRIDMAN networks
Hoang Vinh Dien, Ming-Tuo Zhou, Xin Zhang, Liru Lu (Alina), Masayuki Oodo, Hiroshi Harada
NICT
1. Abstract
Session 6.1.3.4 of SRD IEEE 802.16n-10/0048 specifies the guidelines for path discovery and management.
Based on that, this proposal proposes a framework for establishment and maintenance of alternative paths to
support fast recovery in the event of intermediate note failure or link disconnection. The path calculation
algorithm is out of scope of this proposal. This document is the revised version of original document C80216n11_0026.doc in Session #72, IEEE Singapore plenary meeting.
2. Background
2.1 Introduction
BS
1
2
HR-RS (RS1)
HR-MS
3
HR-RS (MS3)
5
4
HR-MS
6
HR-MS
HR-MS
Figure 1: IEEE 802.16 High reliable relay network tree structure
IEEE 802.16 relay network topology is organized in the tree manner based on the topology information
obtained from topology discovery or update process. Tree topology is centrally determined and managed by the
BS. Relay station (RS) or Mobile stations (HR-MS) in the path from the source MS to the BS will act as the
relay station (HR-RS).
One example of this topology is presented in Fig. 1. In this figure, the HR-BS has a full topology information of
the network. HR-RS1 and HR-MS3 is acting as relay station for mobile node HR-MS4, HR-MS5 and HR-MS6.
HR-RS1 is a pure relay station while as HR-MS3 is a HR-MS acting as a relay station.
If any of HR-RS1 or HR-MS3 fail to operate, Mobile nodes HR-MS4, HR-MS5 and HR-MS6 will be
disconnected from the HR-BS and the network is not high reliable at all. These mobile nodes need to have a
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alternative path to BS to combat the SPOF (Single Pont of Failure) or MPOF (Multi Point of Failure).
Requirements to the alternative path are:
1. Reliable
2. Efficient
3. Simple to calculate
4. Easy to implement and manage.
2.2 A alternative path algorithm for tree topology
Node 1
Node
2
Node
4
Node
3
Node
6
Node
5
Node
7
Node
8
Note:
Node
9
: Tree link
: Direct link
Node
10
Figure 2: A general tree topology
Figure 2 presents a general tree topology. The solid line represents the link belong to the tree topology. The
dotted line represents the direct link between two nodes. However this direct link does not belongs to the tree
topology.
Node 1 is the root node of the topology tree. Furthermore, nodes in the tree topology may have more than one
neighbor nodes. Tree link and direct link represents the fact that nodes are neighbor. For example node 6 has
five neighbor nodes: node 2, node 3, node 5, node 7 and node 10. Node 9 has two neighbor nodes: node 4 and
node 10. The same principle is applied for other nodes.
A backup tree could be easily calculated as follow:
1. Root node of the tree frequently informs all the subordinate nodes about their level in the tree topology.
Level 1 node is nodes that its superordinate node is the root node. Level 2 nodes is nodes that its
superordinate node is level 1 node and so on.
2. All subordinate nodes with level > 1 that does not have backup node to the root node has to put its
neighbors (excluding their superordinate node) in a set named [target backup node] set. Nodes in this
[target backup node] set will be sorted based on the level information in ascending order.
3. The first node in the [target backup node] set will be chosen as the backup node to reach the root node.
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4. When a link or a node in the tree topology fails, the affected nodes will uses their respective backup
nodes to reach the root node. The links to their backup nodes will be used as the new links of the tree.
Node 2 and node 3 are the level 1 nodes because their superordinate node is node 1 – root node. Node 4, node 5,
node 6, node 7 and node 8 are the level 2 nodes because their superordinate nodes are node 2 and node 3
repsprectively – level 1 nodes. Node 9 and node 10 are the level 3 nodes because their superordinate nodes are
node 4 and node 5 respectively – level 2 nodes.
Node 1
Node
2
Node
4
Node
9
Node
5
Node
3
Node
6
Node
7
Node
8
Node
10
Figure 3: Backup nodes selection
Figure 3 illustrates the backup node of tree topology in figure 2. Node 4 has three neighbor nodes: node 2 (level
1), node 5 (level 2) and node 9 (level 3). Target backup node set of node 4 consists of node 5 and node 9. Node
5 will be chosen as the backup node of node 4 since node 5 is the lowest level in the target backup node set –
level 2. The arrow from node 4 to node 5 represents this selection. Same principle is applied for other nodes.
Node 1
Node
2
Node
4
Node
5
Node
3
Node
6
Node
7
Node
8
Note:
Node
9
Node
10
: Tree link
: Direct link
Figure 4: New tree topology after node 3 failure
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Figure 4 illustrates the case when node 3 of the tree topology in figure 2 fails. Node 3 is the superordinate node
of node 7 and node 8. So node 7 and node 8 have to use their backup nodes to reach the root node. From Figure
3, node 7 is node 8’s backup node and node 6 is node 7’s backup node. Hence the backup links from node 8 to
node 7 and from node 7 to node 6 will become the new tree links. A new tree topology is then shown in Figure
4. This new tree topology is formed in very fast manner and helps to maintain the reliability of the network.
3. Alternative path discovery and management in IEEE 802.16n
The algorithm in session 2.2 can be easily applied to the tree topology of 802.16n
3.1 Obtaining network topology
All MS station shall periodically listen to the channel and find out who are its neighboring nodes. This
information shall be send back to the HR-BS in TBD message. Obtaining and determining the tree topology
information follow steps defined in 6.3.21.1 IEEE802.16j document.
3.2 Establishment of alternative path
Alternative path for each subordinate HR-MS shall be determined centrally by HR-BS for both the uplink and
downlink according to session 2.2. This path will be forwarded to the HR-MS in DSA-RSP message.
Once receive the alternative path from HR-BS, HR-MS shall inform all nodes on the alternative path to update
their routing table. Entry in routing table corresponding to alternative path shall be differentiate with normal
routing entry and should not be used in normal circumstances.
3.3 Maintenance of alternative path
When the topology is changed, alternative path should be recalculated to maintain its up to date status and
efficiency. Both BS and MS can decide MS’s current alternative path is still relevant or not. If it’s not, BS shall
construct a new alternative path according to session 2.2, and inform nodes in the new alternative path and old
alternative path for them to update their routing table accordingly.
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3.4 Switch to the alternative path
3.4.1 Preparation
When HR-MS’s timeout with its current main tree exceed the TIME_OUT threshold, it shall inform HR-BS of
this disruption through DSD-REQ message. This DSD-REQ message is sent through the alternative path. This
message also serves as the trigger for nodes in alternative path. Intermediate nodes on the alternative path will
then mark the corresponding alternative entry in their routing table as currently active and shall use this entry to
relay data from/to HR-BS.
3.4.2 Execution
The intermediate nodes in the alternative path should reply the DSD-REQ received from its subordinate node
with DSD-RSP message to confirm that switching to alternative path has been carried out. After receiving
DSD-RSP message from its superordinate, HR-MS shall transmit data to HR-BS through the alternative path
normally.
3.4.3 Refreshing topology information
Once HR-BS receives the topology message from HR-MS, it shall refresh its topology information, build a new
main tree and inform the affected nodes of their new connection identifier (CID).
Once HR-MS receives the new CID from BS, it shall use the new tree for data communication with the BS. It
shall also need to inform nodes on the alternative path of this intention by sending the DSD-REQ message on
the alternative path. Intermediate nodes on the alternative path will then mark the corresponding alternative
entry in their routing table to inactive and shall not use this entry to relay data from/to BS anymore.
4. Text Proposal in IEEE 802.16n AWD
[-------------------------------------------------Start of Text Proposal---------------------------------------------------]
[Insert the following text into Section 17.3.7 Path Discovery and Management of the 802.16n Document
(C802.16n-10/0049)]
17.2.7.1 Alternative Path Establishment Algorithm in a tree topology
In a tree topology, A backup tree could be calculated as follow:
1. Root node of the tree frequently informs all the subordinate nodes about their level in the tree topology.
Level 1 node is nodes that its superordinate node is the root node. Level 2 nodes is nodes that its
superordinate node is level 1 node and so on.
2. All subordinate nodes with level > 1 that does not have backup node to the root node has to put its
neighbors (excluding their superordinate node) in a set named [target backup node] set. Nodes in this
[target backup node] set will be sorted based on the level information in ascending order.
3. The first node in the [target backup node] set will be chosen as the backup node to reach the root node.
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4. When a link or a node in the tree topology fails, the affected nodes will uses their respective backup
nodes to reach the root node. The links to their backup nodes will be used as the new links of the tree.
17.2.7.2 Establishment of Alternative Path
HR-BS determines the tree topology of the network.. From this tree topology, HR-BS shall calculate the
alternative path for HR-MS according to session 17.2.7.1 and inform HR-MS through the messages TBD.
17.2.7.3 Maintenance of Alternative Path
When the topology is changed, alternative path should be recalculated to maintain its up to date status and
efficiency. Both HR-BS and HR-MS can decide HR-MS’s current alternative path is still relevant or not. If it’s
not, HR-BS shall construct a new alternative path according to session 17.2.7.1.
17.2.7.4 Switch to Alternative Path
When HR-MS’s timeout with its current superordinate node exceed the TIME_OUT threshold, it shall establish
connection with its superordinate node in the alternative path through pre-assigned information, and inform HRBS of this disruption through TBD DSD-REQ message. This DSD-REQ message is sent through the alternative
path. This message also serves as the trigger for nodes along the alternative path. Intermediate nodes on the
alternative path will then mark the corresponding backup entry in their routing table as currently active and
shall use this entry to relay data from/to HR-BS.
The intermediate nodes in the alternative path should reply the DSD-REQ received from its subordinate node
with TBD DSD-RSP message to confirm that switching to alternative path has been carried out. After receiving
DSD-RSP message from its superordinate, HR-MS shall transmit data to HR-BS through the alternative path
normally.
Once HR-BS receives the DSD-REQ from HR-MS, it shall refresh its topology information and inform affected
HR-MS about the new topology changes.
[-------------------------------------------------End of Text Proposal----------------------------------------------------]
References
[1] IEEE 802.16n-10/0048, “802.16n System Requirements Document including SARM annex”, January 2011.
[2] IEEE 802.16n-10/0049, “802.16n Table of Contents for Amendment Working Draft”, January 2011.
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